1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus which receives ultrasonic waves applied to, and reflected by a specimen to obtain signals representing the condition of the specimen, and produces a tomogram of a cross section of the specimen on the basis of the signals. More specifically, the present invention relates to an ultrasonic diagnostic apparatus featured by a display that displays a tomogram of a cross section of a specimen, and an ultrasonic diagnostic apparatus capable of calculating the displacement of vital tissues caused by pulsation or an external pressure, and of displaying the result of calculation.
2. Description of the Related Art
An ultrasonic diagnostic apparatus facilitates the diagnosis of diseased parts in a specimen, particularly in human body organs, by receiving ultrasonic waves applied to and reflected by the human body organs to obtain signals representing the condition of the human body organs. The ultrasonic diagnostic apparatus produces a picture of the human body organs on the basis of the signals, and the picture. Methods of determining small displacement of various parts of the human body in addition to producing tomograms have been proposed in, for example, Y. Araki, S. Yagi and K. Nakayama, "Local Displacement Velocity Analysis of Soft Tissue using Doppler Method", Proceedings of the 55th meeting on the Japan Society of Ultrasonics in Medicine, 55-314, PP. 689-690 (December 1989) (reference [1])
The method disclosed in the reference [1] applies a pulse ultrasonic beam to human body organs several times in the same direction and determines the minute displacement of parts at specific depths in the direction of travel of the pulse ultrasonic beam by the pulse Doppler method.
The cross-correlation method is another method of determining a small displacement of the human body (S. Yagi and K. Nakayama, "Local Displacement Analysis of Inhomogenous Soft Tissue by 2-Dimensional Analytic Signal Correlation", Proceedings of the 54th meeting on the Japan Society of Ultrasonics in Medicine, 54-116, pp. 359-360 (May, 1989) (reference [2]).
The cross-correlation method disclosed in reference [2] applies many pulse ultrasonic beams in various directions in the human body, obtains signals corresponding to two tomograms and determines the two-dimensional minute displacement in the human body by calculating a two-dimensional cross-correlation of the signals. The method in reference [2] is also usable in calculating the minute displacement with respect to the depth direction parallel to the scanning line.
Since the determination of the minute displacement is not the subject matter of the present invention, and the cross-correlation method and the pulse Doppler methods are well-known techniques, the description of a method of determining the minute displacement will be omitted.
The subject matter of the present invention is to display the minute displacement determined by the foregoing known methods in a manner useful for diagnosis.
FIGS. 7(A), 7(B) and 7(C) are views of assistance in explaining prior art displaying methods.
FIG. 7(A) is an illustration of a picture displayed by the displaying methods stated in reference [1], in which depth along a scanning line in a tomogram 10 of the human abdomen, having the shades of the diaphragm 11 and a blood vessel 12 is measured on the horizontal axis, minute displacement on the scanning line determined by the prior art method is measured on the vertical axis, and time is measured to an axis perpendicular to a plane defined by the horizontal axis and the vertical axis. It is impossible to recognize all of the minute displacements of the points on the cross section at a glance in the tomogram.
Another displaying method determines the minute displacement of each of the points in a tomogram 10 (each point is represented by a point a) at a moment in which a frame showing the tomogram 10 is formed, represents the minute displacement by a luminance, a value or a chrome of a color, or color variation (hereinafter referred to as "luminance or the like") as shown in FIG. 7(B), superposes the minute displacement of each point represented by a luminance or the like on the tomogram in each frame, and displays frames sequentially as shown in FIG. 7(C).
However, since each point on human body organs moves within a very small time frame, for example, in accordance with a heartbeat, the minute displacement of each point in the tomogram changes very quickly. Therefore, it is difficult to find, or possible to fail in finding an abnormal minute displacement of a point appearing in the tomogram for the diagnosis of a tumor or the like. Therefore, diagnosis using the tomogram requires great skill.
The Doppler method (reference [1]) and the two-dimensional cross correlation (reference [2]) method are representative prior art methods of determining the displacement of each part.
While the Doppler method has the advantages that a displacement can be calculated by the operation of a relatively small operation quantity and the tomogram can be displayed in a real-time mode, the Doppler method is able to calculate only a displacement along the direction of scanning lines. While the two-dimensional cross correlation method is able to calculate a two-dimensional displacement, the two-dimensional cross correlation method needs a large operation quantity in calculating the two-dimensional displacement and is unable to display a tomogram in a real-time mode.